#pragma comment(linker, "/STACK:10000000")
#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <iomanip>
#include <set>
#include <map>
#include <cstdio>
#include <cassert>
#include <string>
#include <cstring>
#define ldb long double
#define ll long long
#define fi first
#define se second
#define fill(a, c) memset(a, c, sizeof(a))
#define sqr(a) ((a) * (a))
#define nextLine() {int c = 0; while((c = getchar()) != 10 && c != EOF);}
#define getBit(mask, k) (((mask) / pw[k]) % pw[1])
#define setBit(mask, k, l) (((mask) / pw[k + 1] * pw[1] + (l)) * pw[k] + ((mask) % pw[k]))
#define debug(a) cerr << #a << " = " << a << " ";
#define debugl(a) cerr << #a << " = " << a << "\n";
#define mp(a, b) make_pair(a, b)
#define pb(a) push_back(a)
#define ff first
#define ss second 
const ldb LDINF = 9128739847123.00;
const ldb eps = 1e-9;
const int inf = 1 << 28;
const ldb pi = fabsl(atan2l(0.0, -1.0));
using namespace std;

string s;
int cnt[123][26];
int res[26];
int n;

void load()
{
	cin >> n;
	for (int i = 0; i < n; i++)
	{
		cin >> s;
		memset(cnt[i], 0, sizeof (cnt[i]));
		for (int j = 0; j < s.size(); j++)
			cnt[i][s[j] - 'a']++;
	}
	memcpy(res, cnt[0], sizeof(cnt[0]));
	for (int i = 1; i < n; i++)
	{
		for (int j = 0; j < 26; j++)
			res[j] = min(res[j], cnt[i][j]);
	}
	s = "";
	for (int i = 0; i < 26; i++)
		s += string(res[i], i + 'a');
	if (s.size() == 0)
		printf("no such string");
	else cout << s;
}

void solve()
{

}

#define file "ana"
int main()
{
	#ifndef ONLINE_JUDGE
		freopen(file".in", "rt", stdin);
		freopen(file".out", "wt", stdout);
	#endif


	load();
	solve();
	return 0;
}
